Some types of driving tools developed in the art comprise a housing, a cylinder that is housed in said housing, a striking piston that moves in a reciprocating manner within the cylinder, and a head valve that opens/closes an upper chamber of the piston with respect to an accumulator. The head valve is situated so as to be located on both the outer circumference of the cylinder as well as the inner circumference of the housing so as to reciprocate in a direction in which the cylinder extends. Furthermore, the head valve is spring-biased by a compression spring that is interposed between a spring guide fixed to the outer circumference of the cylinder and the head valve, in a direction in which the upper chamber of the piston is closed with respect to the accumulator.
A variable pressure chamber and an exhaust chamber are also situated so as to be located on both the outer circumference of the cylinder as well as the inner circumference of the housing. The variable pressure chamber is configured to be in a state where it is opened to the atmosphere so as to apply the pressure of the atmosphere to a pressure-receiving surface of the head valve, or alternately in a state where it supplies compressed air so as to apply the air pressure of the accumulator to the pressure-receiving surface of the head valve. This changeover in state of the variable pressure chamber is performed by an on/off operation of a trigger valve operated by a user via their fingertip. The exhaust chamber is an area to which compressed air discharged from an upper chamber of the piston flows, where said flow is caused by a displacement of the head valve to the closing side after a driving operation. The compressed air flowing to the exhaust chamber is discharged to the outside via an exhaust hole provided on the housing.
In order to open and close the head valve in a smooth manner as well as to prevent exhaust leakage, the variable pressure chamber and the exhaust chamber are required to be separated in a sealed manner with respect to each other at all times. In order to separate the variable pressure chamber from the exhaust chamber, for example, a seal member such as an O-ring is respectively provided on an outer circumferential surface of the head valve facing the housing as well as on an inner circumferential surface of the head valve facing the cylinder. Generally, grease (lubricant) is applied to the seal member in order to provide air-tightness as well as sliding ability. However, high-speed reciprocation of the head valve by compressed air in a driving operation may cause the applied grease to gradually decrease, and hence the wearing resistance of the seal member is greatly reduced, where eventually malfunction of the driving tool may occur.
The variable pressure chamber and the exhaust chamber are narrow portions having relatively small volume and are structurally formed in a dead end manner. Because of this structural configuration, there has existed a problem wherein sufficient grease is not easily applied to the seal member that separates the two chambers in a manufacturing process of the driving tool. One solution has been to contain mist-like lubricant in compressed air to apply lubricant to each part of the driving tool in a maintenance process. However, in this case, it has been difficult to apply sufficient mist-like lubricant to the seal member that separates the variable pressure chamber from the exhaust chamber.
Japanese Patent No. 4507384 discloses a driving tool in which mist-like grease contained in exhaust air from the cylinder is allowed to return to around the seal member. However, in the configuration in which air that contains grease is circulated, which is disclosed, for example, in Japanese Patent No. 4507384, the amount of grease unavoidably decreases compared with that at product shipment and thus replenishment of grease may be required. In contrast, if the driving tool is provided with a grease supplying source from which sufficient grease can be supplied to the seal member disposed on the outer and inner circumferential surfaces of the head valve, a user can save time to replenish grease.
Thus, as a result of the mentioned deficiencies in the art, there is a need in the art to sufficiently lubricate the seal member provided between the head valve and the housing as well as between the head valve and the cylinder in order to improve wear resistance of the seal member and ultimately to improve durability of the driving tool.